Compact capstan

ABSTRACT

A compact capstan includes a drum, a coupled hub, a passage extending through the drum and hub, and a shaft extending through the drum and hub. The shaft engages the passage such that the shaft can transmit a torsional force to the drum and the hub which are free to move along the length of the shaft. The drum includes a spiral groove to receive a cable loop wound around the drum. The hub has a thread with substantially the same pitch as the spiral groove to engage a threaded support such that the hub and the drum move laterally along their length relative to the threaded support as the hub and the drum are rotated. The shaft has a length that is substantially greater than the passage such that the shaft extends beyond both ends of the passage.

FIELD

The embodiments of the invention are generally related to roboticsurgical systems. More particularly, the embodiments of the inventionrelate to cable drive systems for robotic surgical arms.

BACKGROUND OF THE INVENTION

Minimally invasive surgery (MIS) provides surgical techniques foroperating on a patient through small incisions using a camera andelongate surgical instruments introduced to an internal surgical site,often through trocar sleeves or cannulas. The surgical site oftencomprises a body cavity, such as the patient's abdomen. The body cavitymay optionally be distended using a clear fluid such as an insufflationgas. In traditional minimally invasive surgery, the surgeon manipulatesthe tissues using end effectors of the elongate surgical instruments byactuating the instrument's handles while viewing the surgical site on avideo monitor.

A common form of minimally invasive surgery is endoscopy. Laparoscopy isa type of endoscopy for performing minimally invasive inspection andsurgery inside the abdominal cavity. In standard laparoscopic surgery, apatient's abdomen is insufflated with gas, and cannula sleeves arepassed through small (generally ½ inch or less) incisions to provideentry ports for laparoscopic surgical instruments. The laparoscopicsurgical instruments generally include a laparoscope (for viewing thesurgical field) and working tools.

The working tools are similar to those used in conventional (open)surgery, except that the working end or end effector of each tool isseparated from its handle by a tool shaft. As used herein, the term “endeffector” means the actual working part of the surgical instrument andcan include clamps, graspers, scissors, staplers, image capture lenses,and needle holders, for example. To perform surgical procedures, thesurgeon passes these working tools or instruments through the cannulasleeves to an internal surgical site and manipulates them from outsidethe abdomen. The surgeon monitors the procedure by means of a monitorthat displays an image of the surgical site taken from the laparoscope.Similar endoscopic techniques are employed in other types of surgeriessuch as arthroscopy, retroperitoneoscopy, pelviscopy, nephroscopy,cystoscopy, cisternoscopy, sinoscopy, hysteroscopy, urethroscopy, andthe like.

Endoscopy may be performed with robotically controlled working tools.Robotic control may provide an improved control interface to thesurgeon. Robotically controlled working tools may be driven by servomechanisms, such as servo motors, that are coupled to the working toolby mechanical cables. Each servo mechanism may be coupled to a cable bya capstan that draws in and pays out the cable wound around the capstan.The cable may be routed to and from the capstan by one or more pulleys.The cable may rotate a driver that is coupled to the roboticallycontrolled working tool to drive and control movement of the tool. Asspace in the surgical field where robotically controlled working toolsare being used is at a premium, it is desirable to have a compactmechanism to drive and control the robotically controlled working tools.

In a typical cable drive system for a robotically controlled workingtool, a cable is guided by a pulley and wound onto a capstan that isrigidly fixed to a shaft. The capstan being rigidly fixed to the shaftit can only be rotated with the shaft. As a result, the point at whichthe cable comes onto the capstan moves along the length of the capstanas the capstan rotates. If the capstan is close to the pulley guidingthe cable, a large angle can be created in the cable at a take off pointat the capstan. If this angle is too large, the cable may wearexcessively, incur physical damage to its cable strands, run off thetake off pulley, or run out of a groove in the capstan. By increasing adistance between the capstan and the pulley, the angle at the take offpoint may be reduced and be acceptable. However, this makes the cabledrive system less compact. It is desirable to minimize the angle in thecable at the take off point of the capstan while at the same timeproviding a compact mechanism to drive and control movement of arobotically controlled working tool.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a surgical suite in which embodiments of theinvention are used.

FIG. 2 is a pictorial view of a robotic surgical arm and surgicalinstrument from the operating suite of FIG. 1.

FIG. 3 is a plan view of a portion of the robotic surgical arm of FIG. 2that supports the surgical instrument.

FIG. 4 is a schematic of a cable loop that provides lateral motion.

FIG. 5 is a schematic of a cable loop that provides rotary motion.

FIG. 6 is a schematic of another cable loop that provides lateralmotion.

FIG. 7 is a side view of a capstan with a portion of a cable loop.

FIG. 8 is a pictorial view of a portion of the robotic surgical arm ofFIG. 2 that supports the surgical instrument in which a cable drivesystem may be seen.

FIG. 9 is a pictorial view of a portion of FIG. 8 in which the cabledrive system may be seen.

FIG. 10 is a pictorial view of a portion of the cable drive system ofFIG. 9.

FIG. 11 is a plan view of the portion of the cable drive system of FIG.10.

FIG. 12 is a side view of a capstan and take-off pulley.

FIG. 13 is an end view of a compact capstan assembly.

FIG. 14 is a side view of the compact capstan assembly of FIG. 13.

FIG. 15 is a side section view of the compact capstan assembly of FIG.13 along section line 15-15.

FIG. 16 is an end view of another compact capstan assembly.

FIG. 17 is an end view of another compact capstan assembly.

FIG. 18A is a side view of the compact capstan assembly of FIG. 14 at afirst position in a threaded support structure with a portion shown as asection view.

FIG. 18B is a side view of the compact capstan assembly of FIG. 14 at asecond position in the threaded support structure with a portion shownas a section view.

FIG. 19 is an end view of another compact capstan assembly.

FIG. 20 is a side view of another capstan and take off pulley with aportion shown as a section view.

FIG. 21 is a side view of another capstan and take off pulley with asubstantial distance between them.

It will be appreciated that all the drawings of Figures provide forherein are for illustrative purposes only and do not necessarily reflectthe actual shape, size, or dimensions of the elements being illustrated.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description of the embodiments of theinvention, numerous specific details are set forth in order to provide athorough understanding of the embodiments of the invention. However, itwill be obvious to one skilled in the art that the embodiments of theinvention may be practiced without these specific details. In otherinstances well known methods, procedures, components, and circuits havenot been described in detail so as not to unnecessarily obscure aspectsof the embodiments of the invention.

The embodiments of the invention include methods, apparatus, and systemsfor a compact capstan.

In one embodiment of the invention, a method of controlling a cable loopis provided using a slideable capstan. The method includes guiding afirst portion of a cable loop to a slideable capstan using a firsttakeoff pulley and guiding a second portion of the cable loop to theslideable capstan using a second takeoff pulley; coupling the rotationof a shaft to the slideable capstan to rotate the slideable capstan;rotating the shaft in a first direction to draw in the first portion ofthe cable loop and feed out the second portion of the cable loop; and inresponse to the rotation of the capstan, moving the slideable capstanalong the shaft to substantially maintain the positions of the firsttakeoff point and the second takeoff point relative to the first takeoffpulley and the second takeoff pulley, respectively.

In another embodiment of the invention, a capstan drive is provided thatincludes a cable receiving means to receive a cable loop; a moving meansto move a take off point of the cable receiving means laterally as thecable receiving means is rotated; and a transmitting means to transmit atorsional force to rotate the cable receiving means. As the cablereceiving means is rotated it is free to move laterally with respect tothe transmitting means.

In another embodiment of the invention, a compact capstan drive isprovided including a capstan support, a motor coupled to the capstansupport, and a capstan coupled to the threaded portion of the capstansupport. The capstan support has a threaded portion to receive a hub ofthe capstan. The motor has a drive shaft with an axis of rotation torotate the capstan. The capstan includes a drum, a hub coupled to thedrum, and a shaft coupled to the drive shaft of the motor. The drum ofthe capstan has a spiral groove on a cylindrical surface to receive acable loop wound around the drum. The hub has a thread to engage thethreaded portion of the capstan support. As the hub and the drum arerotated together, they move laterally along their length relative to thethreaded support. The shaft of the capstan engages the drum and the hubto transmit a torsional force to rotate the drum and the hub. As theyrotate, the drum and the hub are free to move along the length of theshaft.

In another embodiment of the invention, a compact capstan is providedincluding a drum, a threaded hub, and a shaft rotatably supported in afixed relationship to a threaded support. The drum has a cylindricalsurface, a first end, and an opposite second end. The cylindricalsurface of the drum has a spiral or helical groove to receive a cableloop that is wound around the drum. The threaded hub is coupled to thefirst end of the drum and engages the threaded support. The threaded huband the drum move together laterally along their length relative to thethreaded support in response to their being rotated. The shaft engagesthe drum and the hub to transmit a torsional force to rotate the drumand the hub. The drum and the hub are free to move along the length ofthe shaft as they are rotated.

The detailed description describes the invention as it may be used in alaparoscopic surgery. It is to be understood that this is merely oneexample of the types of surgeries in which the invention may be used.The invention is not limited to laparoscopy nor to the particularstructural configurations shown which are merely examples to aid in theunderstanding of the invention. Traditional minimally invasive surgeryrequires a high degree of surgical skill because the surgeon's handmovements are controlling a surgical tool at a substantial distance fromthe surgeon's hands, often requiring unnatural and non-intuitive handmotions. In robotically assisted surgery, a surgeon may operate a mastercontroller to control the motion of surgical instruments at the surgicalsite. Servo mechanisms may move and articulate the surgical instrumentbased on the surgeon's manipulation of the hand input devices. Therobotic assistance may allow the surgeon to control the motion ofsurgical instruments more easily and with greater precision.

FIG. 1 shows a schematic plan view of a surgical suite in which theinvention may be used. A patient 110 is shown on an operating table 112undergoing robotically assisted laparoscopic surgery. A surgeon 120 mayuse a master controller 122 to view a video image of the internalsurgical site and control one or more surgical instruments and alaparoscopic camera by means of robotic servo mechanisms. The mastercontroller 122 will typically include one or more hand input devices(such as joysticks, exoskeletal gloves, or the like) which are coupledby a servo mechanism to a surgical instrument. One or more roboticsurgical arms 100, 102 may be used to support and move surgicalinstruments 104 at the surgical site during robotically assistedsurgery.

FIG. 2 shows a robotic surgical arm 102 supporting a surgical instrument104. The surgical instrument 104 may include a head end 200 coupled toan end effector 204 by a tool shaft 202. The end effector 204 may beinserted into a surgical site through a cannula 206 that is supported bythe robotic surgical arm 102. The end effector 204 at an internal end ofthe tool shaft 202 may provide any of a variety of surgical tools whichmay be actuated by servo mechanisms 210 which may be supported by therobotic surgical arm 102. The end effector 204 is coupled to a head end200 of the surgical instrument 104 through the tool shaft 202. The headend 200 may include one or more drivers that control the movement of theend effector 204. Rotation of the drivers may be used to control themovement of the end effector 204.

The head end 200 of the surgical instrument 104 may be coupled to a toolcarriage 220 on the robotic surgical arm 102. This may facilitateexchange of the surgical instrument 104 during the course of a surgicalprocedure. The tool carriage 220 may be slidingly supported by a spar222 that is supported by the robotic surgical arm 102. The tool carriage220 may be moved along the spar 222 to change the depth of insertion ofthe end effector 204 by moving the entire surgical instrument 104.

Referring to FIGS. 1 and 2, the robotic surgical arm 102 may include oneor more servo motors 210 to move the surgical instrument 104 and/or theend effector 204 on the surgical instrument. One or more control wires124 may provide signals between the computer 123 in the mastercontroller 122 and the servo motors 210 on the robotic surgical arm 102.The master controller 122 may include a computer 123 to provide signalsthat control the servo mechanisms 210 of the surgical instrument 104based on the surgeon's input and received feedback from the servomechanisms.

FIG. 3 shows the spar 222, the tool carriage 220, and the servo motors210 removed from the robotic surgical arm. The servo motors 210 may movethe tool carriage 220 laterally along the spar 222. Movement of the toolcarriage 220 along the spar 222 controls the depth of insertion of thesurgical instrument that is connected to the tool carriage. The servomotors 210 may further move the end effector 204.

The end effector 204 may be moved by rotating receiving elementsprovided in the head end 200 of the surgical instrument 104. Eachreceiving element of the surgical instrument 104 may be coupled to arotatable driver 324 provided on the tool carriage 220. The end effector204 may be arranged such that approximately one revolution or less ofthe rotatable driver 324 moves the controlled motion of the end effector204 through its full range. Thus, one or more servo motors 210 may becoupled to the surgical instrument 104 to control a motion of the endeffector 204 or a rotation of the tool shaft 202.

FIG. 4 shows a schematic of a cable loop 400 that may be used to providethe lateral motion of the tool carriage 220 along the spar 222. For thepurposes of this invention, a cable loop is used to describe amechanical power transmission by means of a long flexible “cable”, suchas a wire or fiber cable or a thin flexible belt or band, that is drivensuch that one part of the cable is drawn in by the driving mechanismwhile an equal amount of the cable is fed out. This results in a motionof the cable comparable to the motion of a continuous loop of cable.However, for the purposes of this invention, the “cable loop” need notphysically be in the form of a continuous loop of cable. The cable mayalso be tubing that transports fluids or gases to or from the surgicaltool.

As shown in FIG. 4, the “cable loop” 400 may advantageously be providedby one or more cable segments 402, 404 that are coupled to provide themotion of a continuous loop of cable. In the schematic cable loop 400 ofFIG. 4, the cable loop is provided by two cable segments 402, 404 eachof which has an end 406, 408 that is coupled to the tool carriage 220.As a first end 410 of the cable is drawn in, a second end 412 of thecable is fed out and passed around an outboard pulley 414. Thisarrangement provides a controlled lateral movement of the tool carriage220.

FIG. 5 shows a schematic of a cable loop 500 that may be used to providethe rotary motion of a rotatable driver 324. A single cable segment isshown with each of the two ends 502, 504 coupled to one of two coupleddriver pulleys such that the pulleys are rotated as a first portion 508of the cable 500 is drawn in while a second portion 510 of the cable isfed out and passed around an outboard pulley 514. It will be appreciatedthat two or more cable segments could be used to control the rotation ofthe rotatable driver 324 in an arrangement similar to that shown in FIG.4. Likewise, a single cable segment in the arrangement shown in FIG. 5could be used to control lateral movement of the tool carriage 220.

FIG. 6 shows a schematic of a cable loop 600 that may be used to providea lateral movement of the tool carriage 220. The first 602 and second604 ends of the cable loop 600 are wound around a capstan 606 andsecured thereto. The capstan 606 provides a positive drive for drawingin a first portion 608 of the cable loop 600 while feeding out a secondportion 609 of the cable at the same rate. The capstan 606 furtherprovides spooling of the cable loop 600 as it is drawn in and unspoolingof the cable as it is fed out. Two take off pulleys 610, 612 may beprovided adjacent the capstan 606 to provide a stable path for the cableloop 600 as it passes to the outboard pulley 614 and to the toolcarriage 220. Each end 602, 604 of the cable loop 600 may make one ormore turns around the capstan 606 and then pass around one of the takeoff pulleys 610, 612 adjacent the capstan. Additional pulleys (notshown) may be provided between the take off pulleys 610, 612 and thetool carriage 220 to direct the cable loop 600 as required.

FIG. 7 shows a side elevation of the capstan 606 and a portion of thecable loop 600. The portions of the cable 608, 609 that extend to thetake off pulleys 610, 612 have been shown as extending to the sides sothat the point of take off 616 from the capstan 606 can be more easilyseen. The point at which one end 604 of the cable may be secured to thecapstan 606 is visible while the other end 602 of the cable may besecured to the capstan at the opposite end and on the opposite side suchthat it is not visible in this elevation. Alternatively, the cable maybe attached at different places on the capstan or may not be attached tothe capstan.

A coupled device, such as the tool carriage 220 or the rotatable driver324, may be moved by rotating the capstan 606 to cause one portion 608of the cable loop 600 to be drawn in and wound onto the capstan whileunwinding and feeding out a second portion 609 of the cable loop. Thecapstan 606 may include a spiral or helical groove having a shape thatreceives the cable as it is wound onto the capstan. The spiral orhelical groove may have a pitch, longitudinal spacing of adjacentsections of the groove, that allows the cable to be wound onto thecapstan without overlaying adjacent turns of the cable. It will beappreciated that the take off point 616 for the cable loop 600 will movelaterally along the capstan 606 as the cable is wound onto and aroundthe capstan.

FIG. 8 shows a pictorial view of the spar 222, the tool carriage 220,and the servo motors 210 with the supporting structure removed so thatcapstans 800 which are driven by the servo motors may be seen. Thecapstans 800 are illustrated facing upward for clarity but they wouldtypically face downward toward the patient in use. FIG. 9 shows a closerview of just the portion with the capstans 800. Five servo motors areshown driving five capstans. Two take off pulleys are provided for eachcapstan. Additional pulleys are provided to guide the cable through thespar.

Referring to FIG. 8, each of the servo motors 210 may provide a rotarymotion that is coupled to the tool carriage 220 by a cable loop 830. Forexample, the cable loop 830 may pass over a pulley 832 at the end of thespar 222 remote from the servo motors 210. One of the instrument drivers324 (see FIG. 3) on the tool carriage 220 may be coupled to the cableloop 830 such that movement of the cable loop by one of the servo motors210 rotates the instrument driver. Additional cable loops (not shown)may be coupled to the remaining instrument drivers 324 on the toolcarriage and to the tool carriage 220 itself such that movement of theadditional cable loops by the associated servo motors 210 rotates theremaining drivers and moves the tool carriage along the spar 222.

Each servo motor 210 may drive one of the capstans 800, possibly througha gearbox (not shown). It may be appreciated from FIG. 8, which showsfive servo motors 210 with their associated capstans and take offpulleys and additional pulleys for guiding the cables, that space is ata premium.

Referring to FIG. 9, it will be seen that the cables are directed fromthe capstans toward the spar (not shown) which is located toward theleft in FIG. 9. Two of the capstans 904, 906 are adjacent the spar, twocapstans 908, 910 are remote from the spar, and a fifth capstan 902 isbetween the other four capstans. For a capstan 908 that is remote fromthe spar, the take off pulleys 912, 914 may be a substantial distancefrom the capstan.

As shown in FIG. 21, the lateral shift in the take off point 2106 of thecable loop 2100 from the capstan 908 as the cable loop is wound andunwound from the capstan creates only an acceptably small angle 2104between the portion of the cable loop extending to the take off pulley914 and the plane 2102 of the take off pulley, even when the cable is atthe extremes of its travel on the capstan. A small angle 2104 betweenthe cable 2100 and the plane 2102 of the take off pulley 914 isacceptable. An angle of approximately five degrees may be acceptable fora typical configuration.

In contrast, the remaining three capstans 902, 904, 906 are close totheir take off pulleys 916, 918, 920, 922, 1024, 1026 that receive thecable loops from these capstans.

FIG. 10 shows these three capstans and their take off pulleys. FIG. 11is a plan view of these three capstans and their take off pulleys whichshows the short distance between the capstan and the take off pulleys.The distance between each capstan and its associated take off pulleysmay be comparable to the distance between the take off points when thecable is at the extremes of its travel on the capstan.

FIG. 12 is a side elevation of a capstan 904 that is close to its takeoff pulley 922. This creates a relatively large angle 1204 between thecable 1200 and the plane 1202 of the take off pulley 922 when the cableis at the extremes of its travel on the capstan 904. It will beappreciated that a large angle 1204 between the cable 1200 and the plane1202 of the take off pulley 922 causes unbalanced forces on the take offpulley that can increase friction and cause wear in the system. The sizeof angle 1204 between the cable 1200 and the plane 1202 of the take offpulley 922 that becomes unacceptable depends on a variety of factors,such as the load on the cable and configuration of the pulleys. Thecable 1200 may run off the capstan groove or the take off pulley 922 ifthe angle between the cable and the plane of the take off pulley 1202 istoo great. An angle 1204 between the cable 1200 and the plane 1202 ofthe take off pulley 922 increases the length of the cable loop, whichmay require some form of tension compensating device. The capstan 904and take off pulley 922 configuration shown may be unworkable if thecable 1200 is allowed to form the angle 1204 shown to the plane 1202 ofthe take off pulley 922.

FIGS. 13 through 15 show a compact capstan 1300 with FIG. 13 being anend view, FIG. 14 being a side view, and FIG. 15 being a sectioned viewfrom the side. The compact capstan 1300 includes a drum 1310 that isgenerally in the form of a cylinder having a cylindrical surface 1302, afirst end 1304, and an opposite second end 1306. A spiral or helicalgroove 1308 is provided in the cylindrical surface 1302 of the drum intowhich a cable loop may be wound. The cable loop may be discontinuouswith two ends of segments of the cable loop being secured to oppositeends 1312, 1318 of the spiral or helical groove 1308. This configurationof the cable loop may permit the two segments of the cable loop to takeoff from the capstan at approximately the same lateral position alongthe length of the drum as may be seen in FIG. 10.

A threaded hub 1314 is coupled to the first end 1304 of the drum 1310.The threaded hub 1314 may include a synchronization thread withsubstantially the same pitch as the spiral or helical groove 1308. Inthe configuration shown, the thread is an external thread but aninternal thread may be used in other configurations. The thread may be asixty degree Unified National thread, a metric thread, an Acme thread,or other form of screw thread.

As shown in FIGS. 18A and 18B, the threaded hub 1314 engages a threadedsupport 1800. As the threaded hub 1314 and the drum 1310 are rotated,they move laterally along their length relative to the threaded support1800. As discussed further below, this may maintain a substantiallyconstant angle between the cable and the plane of the take off pulley.

A splined passage 1500 extends through the drum 1310 and threaded hub1314 from an end 1306 of the drum to an opposing end 1316 of the hub. Asplined shaft 1330 has a length that is greater than a length of thesplined passage 1500. The splined shaft 1330 passes through the splinedpassage 1500 extend. The splined shaft 1330 extends beyond both ends1206, 1316 of the splined passage 1500. The splined shaft 1330 transmitsa torsional force to the drum 1310 and the threaded hub 1314 whichremain free to move laterally along the splined shaft.

The splined shaft 1330 may provide one or more grooves 1832 orprojections that extend along the length of the splined shaft. Thesplined passage 1500 may provide one or more projections or grooves thatmate with the respective grooves or projections of the splined shaft1330 to provide positive transmission of torsional forces to the drum1310 and the threaded hub 1314.

A particularly advantageous form of splined shaft and passage for use inthe present invention is a ball spline assembly. As may be seen in FIG.15, a ball spline assembly may include a splined shaft 1330 and a ballspline nut 1502. The ball spline nut may include a number ofrecirculating balls 1500 as the projections that mate with a groove 1832in the splined shaft 1330. Ball spline assemblies provide nearlyfriction-free linear motion while simultaneously transmitting torsionalloads. The spline nut 1502 may be preloaded to decrease the radial playin the ball spline assembly and provide low backlash.

FIG. 15 is a section view of the side elevation of the compact capstanassembly 1300. A portion 1504 of the splined passage 1500 that is withinthe drum 1310 may be enlarged to receive the spline nut 1502, which mayhave a diameter that is similar to the diameter of the hub portion 1314.The spline nut 1502 may be fixed within the splined passage 1500 by anyof a variety of means, such as a set screw. The spline nut 1502 may movein unison with the drum 1310. The portion of the splined passage 1500within the threaded hub 1314 may have a diameter that is only sufficientto receive the splined shaft 1330.

FIG. 16 shows an end view of a hub 1600 that includes a conventionalsplined passage 1602. FIG. 17 shows an end view of a hub 1700 thatincludes a hexagonal shaped passage 1702. It will be appreciated thatthe shaft and passage can take any of a variety of forms. The passagewill engage the shaft such that the shaft can transmit a torsional forceto the drum and the hub which are free to move along the length of theshaft.

FIGS. 18A and 18B show a compact capstan assembly 1300 in a threadedsupport structure 1800. The threaded support structure 1800 provides athreaded passageway 1806 to receive the threaded hub 1314 of the capstanassembly 1300. The threaded support structure 1800 may also support amotor assembly 210, two take off pulleys 1802, 1804, and the end 1334 ofthe splined shaft 1330 that emerges from the drum end 1306 of thecapstan assembly 1300. The portion of the threaded support structure1800 providing the threaded passageway 1806 and the support and coupling1810 of the motor assembly 210 are shown in cross-section along thediameter of the threaded passageway and the remainder of the elementsare shown in full elevations.

The motor assembly 210 may include a gear box such that the shaft thatemerges from the assembly provides a higher torque and a slowerrotational speed than the shaft of the motor itself. The splined shaft1330 is fixedly coupled to a shaft of the motor assembly 210 such thatthe splined shaft is an extension of the motor assembly shaft. It may beappreciated that the threaded support structure 1800 may hold all thecomponents in a fixed relationship to one another except for the compactcapstan assembly 1300.

As may be seen in FIGS. 18A and 18B the threaded hub 1314 and drum 1310move laterally along the length of the splined shaft 1330 as the capstanassembly 1300 is rotated. This is because the threads of the hub 1314couple to the threaded passageway 1806 of the threaded support structure1800. FIGS. 18A and 18B may represent the two extremes of travel of thethreaded hub 1314 and drum 1310 with respect to the support structure.

It will be seen that the take off point 1808A, 1808E for the cable movesalong the length of the drum 1310 as the drum rotates between the twoextremes of travel. It will further be seen that the drum 1310 moveslaterally at a similar rate as the take off point 1808A, 1808E for thecable moves because the threaded hub 1314 has substantially the samepitch as the spiral or helical grove 1308 on the drum 1310 in which thecable is wound. As a result, the take off point 1808A, 18088 for thecable remains at substantially the same lateral position relative to thethreaded support structure 1800 and more particularly relative to thetake off pulleys 1802, 1804. This permits the take off pulleys 1802,1804 to be placed a short distance away from the capstan 1300 becauserotation of the capstan will not result in a large angle between thecable and the plane of the take off pulleys. Moreover the angle betweenthe cable and the plane of the take off pulleys may be essentiallyconstant over the entire range of motion of the compact capstan 1300.

The take off pulleys 1802, 1804 and the splined shaft 1330 are coupledto the threaded support structure 1800 so they are free to rotate whilebeing constrained against lateral movement. It will be appreciated thatonly the threaded hub 1314, drum 1310, and spline nut 1502 can movelaterally relative to the threaded support structure 1800. This maysimplify the connection between the motor assembly 210 and the capstanassembly 1300 because the motor assembly may be coupled to the splinedshaft 1330 and supported by the threaded support structure 1800. This ispossible because there is no lateral motion of the splined shaft 1330relative to the motor assembly 210 or the threaded support structure1800.

FIG. 19 shows an end view of a capstan and shaft assembly 1900 thatprovides another form of coupling between the capstan 1902 and the shaft1904. A disk-like flexure 1906 is attached to the capstan at the outsidediameter of the flexure. The shaft 1904 passes through a central hole inthe flexure 1906 and is attached to the flexure along the edge of thecentral hole. The flexure 1906 has a series of spokes that join theinner and outer portions of the flexure. The spokes make the flexure1906 compliant along the axis of the shaft 1904 while maintaining a hightorsional stiffness. Thus the shaft 1904 can transmit a torsional forceto the drum and the hub of the capstan 1902 which is free to move alongthe length of the shaft within the limits of the flexure's 1906 axialcompliance.

The flexure 1906 may provide a limited range of axial motion as comparedto configurations that use a splined shaft. Configurations employing aflexure 1906 to couple the capstan 1902 to the shaft 1904 may onlyprovide a moderate shifting of the capstan. In some configurations thehub may have a smaller pitch than the groove in the hub. Thus thecapstan will slide to reduce some but not all of the angle between thecable and the plane of the take off pulley. This may maintain the anglewithin an acceptable range. An angle of approximately five degrees maybe acceptable for a typical configuration.

Two flexures 1906, spaced some distance apart, may couple the capstan1902 to the shaft 1904. This may provide radial support for the capstan1902.

In another configuration, a single flexure 1906 may couple the capstan1902 to the shaft 1904 at one end of the capstan 1902. The capstan 1902may include a passage with a slip fit on the shaft that enables axialsliding and provides radial support.

FIG. 20 shows another compact capstan assembly 2000 in a threadedsupport structure 2050. The threaded support structure 2050 provides athreaded post 2014 that engages a threaded passageway of the capstanassembly 2000. The threaded support structure 2050 may also support amotor assembly 2060, and two take off pulleys 2002, 2004.

In comparison to the threaded support structure 1800 shown in FIGS. 18Aand 18B, the threaded post 2014 in the configuration shown in FIG. 20 ison the opposite side of the support structure 2050 from the motorassembly 2060.

In the configuration shown, the shaft 2020 of the motor assembly 2060 iscoupled to the capstan 2000 by a bellows 2030. The bellows can transmita torsional force to the drum and the hub of the capstan 2000 which isfree to move along an axis defined by the motor shaft 2020 within thelimits of the bellows' extension.

It may be appreciated that the threaded support structure 2050 may holdall the components in a fixed relationship to one another except for thecompact capstan assembly 2000. The capstan 2010 moves laterally alongthe length of threaded post 2014 as the capstan assembly 2000 isrotated. As in the previous configuration, the take off point 2008 forthe cable remains at substantially the same lateral position relative tothe threaded support structure 2050 and, more particularly, relative tothe take off pulleys 2002, 2004. Only the capstan assembly 2000 moveslaterally relative to the threaded support structure 2050.

In another configuration (not shown), the threaded support structureprovides a threaded passageway rather than a threaded post on theopposite side of the support structure from the motor assembly. Thecompact capstan assembly in this configuration may be similar to thecompact capstan assembly 1800 shown in FIGS. 18A and 18B. However, thethreaded passageway supports the threaded hub that, in turn, supportsthe outboard end of the splined shaft. This may eliminate the need foran outboard bearing to support the outboard end of the splined shaft.

While certain exemplary embodiments have been described and shown in theaccompanying drawings, it is to be understood that such embodiments aremerely illustrative of and not restrictive on the broad invention. Forexample, while an externally threaded hub is shown coupled to aninternally threaded passage in the support structure, the capstan mayprovide an internally threaded hub that is coupled to a threaded post onthe support structure. This invention is not limited to the specificconstructions and arrangements shown and described, since various othermodifications may occur to those ordinarily skilled in the art.

1.-28. (canceled)
 29. A compact capstan comprising: a drum having acylindrical surface, a first end, and an opposite second end, thecylindrical surface of the drum having a spiral groove to receive acable loop wound around the drum; a threaded hub coupled to the firstend of the drum, the threaded hub to engage a threaded support, thethreaded hub and the drum to move together laterally along their lengthrelative to the threaded support in response to being rotated; a ballspline nut coupled to the drum and the hub; and a splined shaftrotatably supported in a fixed relationship to the threaded support, thesplined shaft engaging the ball spline nut to transmit a torsional forceto rotate the drum and the hub, the ball spline nut, the drum and thehub being free to move along the length of the splined shaft.
 30. Thecompact capstan of claim 29, wherein the ball spline nut has a diameterthat is similar to a diameter of the hub and the ball spline nut islocated substantially within the drum.
 31. The compact capstan of claim29, wherein the drum further includes two cable attachment points, eachcable attachment point being at an end of the spiral groove forreceiving an end of a segment of the cable loop.
 32. The compact capstanof claim 29, wherein the drum and hub include a passage extending froman end of the drum through to an end of the hub furthest from the drum,and the shaft has a length that is substantially greater than a lengthof the passage, the shaft passing through the passage and extendingbeyond both ends of the passage.
 33. The compact capstan of claim 29,the hub includes a thread with substantially the same pitch as thespiral groove of the drum.
 34. A compact capstan drive comprising: acapstan support having a threaded portion; a motor coupled to thecapstan support, the motor having a drive shaft with an axis ofrotation; and a capstan coupled to the threaded portion of the capstansupport, the capstan including a drum having a spiral groove on acylindrical surface, the spiral groove to receive a cable loop woundaround the drum; a hub coupled to the drum, the hub having a thread toengage the threaded portion of the capstan support, the hub and the drumto move laterally along their length relative to the threaded support inresponse to being rotated; a ball spline nut coupled to the drum and thehub; and a splined shaft coupled to the drive shaft of the motor, thesplined shaft engaging the ball spline nut to transmit a torsional forceto rotate the drum and the hub, the ball spline nut, the drum, and thehub being free to move along the length of the splined shaft.
 35. Thecompact capstan drive of claim 34, wherein the ball spline nut has adiameter that is similar to a diameter of the hub and the ball splinenut is located substantially within the drum.
 36. The compact capstandrive of claim 34, wherein the drum further includes two cableattachment points, each cable attachment point being at an end of thespiral groove for receiving an end of a segment of the cable loop. 37.The compact capstan drive of claim 34, further comprising two take offpulleys rotatably coupled to the support structure.
 38. The compactcapstan drive of claim 34, wherein the spiral groove of the drum hassubstantially the same pitch as the threaded passage.
 39. The compactcapstan drive of claim 34, wherein the drum and the hub include apassage extending from an end of the drum through to an end of the hubfurthest from the drum, and the shaft has a length that is substantiallygreater than a length of the passage, the shaft passing through thepassage and extending beyond both ends of the passage.
 40. A compactcapstan drive comprising: a cable receiving means to receive a cableloop; a moving means to move a take off point of the cable receivingmeans laterally as the cable receiving means is rotated; and atransmitting means to transmit a torsional force to rotate the cablereceiving means, as it is rotated the cable receiving means is free tomove laterally with respect to the transmitting means, the transmittingmeans including a splined shaft and a ball spline nut that engages thesplined shaft.
 41. The compact capstan drive of claim 40, wherein theball spline nut is located substantially within the cable receivingmeans.
 42. The compact capstan drive of claim 40, wherein the cablereceiving means further includes an end receiving means to receive anend of a segment of the cable loop.
 43. The compact capstan drive ofclaim 40, further including a providing means to provide the torsionalforce to the cable receiving means.
 44. The compact capstan drive ofclaim 40, further including a supporting means to support the providingmeans and the cable receiving means, wherein the providing means beingfixed to the supporting means and the cable receiving means being fixedaxially but not laterally to the supporting means.
 45. The compactcapstan drive of claim 44, further including a guiding means to guidethe cable loop to and from the cable receiving means.
 46. The compactcapstan drive of claim 45, wherein the guiding means is fixed laterallyto the supporting means.
 47. A method of controlling a cable loop, themethod comprising: receiving the cable loop in a spiral groove on acylindrical surface of a drum; rotating a splined shaft that engages aball spline nut coupled to the drum to transmit a torsional force whileleaving the drum free to move laterally on the splined shaft; and movingthe drum laterally on the splined shaft by a threaded hub coupled to thefirst end of the drum, the threaded hub engaging a threaded support suchthat the ball spline nut, the threaded hub and the drum move togetherlaterally along their length relative to the threaded support inresponse to the ball spline nut, the threaded hub and the drum beingrotated by the splined shaft.
 48. The method of claim 47, furtherincluding guiding the cable loop to and from the drum with two takeoffpulleys, one end of the loop portion of the cable loop extending from afirst of the two take off pulleys and the opposite end of the loopportion of the cable loop extending from a second of the two take offpulleys.
 49. The method of claim 47, further including energizing amotor coupled to the splined shaft to rotate the splined shaft.